Method of making a semiconductor device using a silicon carbide hard mask

ABSTRACT

A method of converting a hydrophobic surface of a silicon carbide layer to a hydrophilic surface is described. That method comprises forming a silicon carbide containing layer on a substrate, then operating a PECVD reactor to generate a plasma that converts the surface of that layer from a hydrophobic surface to a hydrophilic surface. Also described is a method for making a semiconductor device that employs this technique.

FIELD OF THE INVENTION

[0001] The present invention relates to a method of making semiconductordevices using a silicon carbide hard mask.

BACKGROUND OF THE INVENTION

[0002] Semiconductor devices include metal layers that are insulatedfrom each other by dielectric layers. As device features shrink,reducing the distance between the metal layers and between metal lineson each layer, capacitance increases. To address this problem,insulating materials that have a relatively low dielectric constant arebeing used in place of silicon dioxide to form the dielectric layer thatseparates the metal lines.

[0003] Certain materials that may be used to form low k dielectriclayers (e.g., those comprising organic polymers) must be protected, whencertain processes are used to remove photoresist, or other substances,from their surfaces. In a commonly used technique to protect suchmaterials, a hard mask is formed on their surface prior to depositingphotoresist, or other substances, on top of them. Such a hard mask maybe formed from silicon carbide. Although silicon carbide may adequatelyprotect an underlying dielectric layer during subsequent process steps,this class of materials is hydrophobic. Silicon carbide's hydrophobicnature renders it difficult to clean its surface, and to bond it toother layers. In addition, materials that are coated onto siliconcarbide may lack desirable thickness uniformity.

[0004] Current methods for addressing silicon carbide's undesirableattributes employ adhesion promoters and certain chemical solutions,which modify surface chemistry to facilitate surface cleaning. Suchmethods require the use of relatively expensive chemicals. Accordingly,there is a need for an improved process for making a semiconductordevice using a silicon carbide hard mask. There is a need for such aprocess that converts a hydrophobic silicon carbide surface to ahydrophilic one in a relatively inexpensive and unobtrusive manner,enabling improved adhesion characteristics and facilitating surfacecleaning. The method of the present invention provides such a process.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIGS. 1a-1 d represent cross-sections of structures that mayresult after certain steps are used to make a semiconductor device in aprocess that may benefit from application of the method of the presentinvention.

[0006]FIG. 2 provides a schematic representation of a CVD chamber for aPECVD reactor.

[0007]FIGS. 3a-3 c represent cross-sections of structures that mayresult after certain steps are used to make a semiconductor device in asecond process that may benefit from application of the method of thepresent invention.

[0008]FIGS. 4a-4 e represent cross-sections of structures that mayresult after certain steps are used to make a semiconductor device in athird process that may benefit from application of the method of thepresent invention.

[0009]FIG. 5 represents a cross-section of a structure that includes asilicon carbide layer deposited on a substrate, which may benefit fromapplication of the method of the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0010] A method is described for converting a hydrophobic surface of asilicon carbide layer to a hydrophilic surface. That method comprisesforming a silicon carbide containing layer on a substrate, thenoperating a plasma enhanced chemical vapor deposition (“PECVD”) reactorto generate a plasma that converts the surface of that layer from ahydrophobic surface to a hydrophilic surface. In a preferred embodimentof the present invention, the reactor is first operated to form thesilicon carbide containing layer on the substrate. It is then operatedto generate the plasma that converts the surface of that layer from ahydrophobic surface to a hydrophilic surface while the substrate remainsin situ inside the reactor.

[0011] In the following description, a number of details are set forthto provide a thorough understanding of the present invention. It will beapparent to those skilled in the art, however, that the invention may bepracticed in many ways other than those expressly described here. Theinvention is thus not limited by the specific details disclosed below.

[0012] The method of the present invention may be used in many contexts.For example, this method may be used when making a semiconductor device,e.g., being applied to convert a hydrophobic surface of a siliconcarbide hard mask into a hydrophilic surface—which can better adhere tomaterials that are coated onto it and which can be more easily cleaned.FIGS. 1a-1 d represent cross-sections of structures that may be formedwhen making a semiconductor device using the method of the presentinvention. FIG. 1a represents a structure that includes substrate 100upon which is formed a first conductive layer 101. First conductivelayer 101 is covered by barrier layer 102, which in turn is covered bydielectric layer 103. Hard masking layer 104 covers dielectric layer103.

[0013] Substrate 100 may be any surface, generated when making anintegrated circuit, upon which a conductive layer may be formed.Substrate 100 may include, for example, active and passive devices thatare formed on a silicon wafer such as transistors, capacitors,resistors, diffused junctions, gate electrodes, local interconnects,etc. . . . Substrate 100 also may include insulating materials thatseparate such active and passive devices from the conductive layer orlayers that are formed on top of them, and may include previously formedconductive layers.

[0014] Conductive layer 101 may be made from materials conventionallyused to form conductive layers for semiconductor devices. Barrier layer102 serves to prevent an unacceptable amount of the material included inconductive layer 101 from diffusing into dielectric layer 103. Barrierlayer 102 also acts as an etch stop to prevent a subsequent via etchstep from exposing conductive layer 101 to subsequent cleaning steps.Barrier layer 102 preferably is made from silicon nitride or siliconcarbide, but may be made from other materials that can serve suchfunctions, as is well known to those skilled in the art.

[0015] In this embodiment, dielectric layer 103 comprises a low-kmaterial, e.g., a material with a dielectric constant less than about3.0, which must be protected when photoresist—to be coated on top ofit—is removed. Dielectric layer 103 may, for example, comprise SiOF oran organic polymer—such as a polyimide, parylene, polyarylether,polynaphthalene, or polyquinoline. Commercially available polymers soldby Honeywell, Inc., under the trade name FLARE™, and by the Dow ChemicalCompany, under the trade name SiLK™, may be used to form dielectriclayer 103. Hard masking layer 104 is formed on dielectric layer 103 inthe conventional manner and comprises silicon carbide. In addition tosilicon carbide, layer 104 may include some hydrogen—depending upon howlayer 104 is made. The structure shown in FIG. 1a may be generated usingconventional process steps, as will be apparent to those of ordinaryskill in the art.

[0016] Because the surface of silicon carbide hard masking layer 104 ishydrophobic, it has poor adhesion qualities and is difficult to clean.By applying the method of the present invention to that surface,however, it may be converted to a hydrophilic surface that may bondbetter to photoresist and be easier to clean. In that method, thestructure shown in FIG. 1a may be formed in a PECVD reactor, e.g., PECVDreactor 200 illustrated in FIG. 2. While the FIG. 1a structure remainsin situ inside the reactor, that reactor is then operated to generate aplasma that converts the surface of silicon carbide hard masking layer104 from a hydrophobic surface to a hydrophilic surface. Althoughpreferably retaining the wafer in situ inside the reactor when formingthe silicon carbide layer and converting its surface to a hydrophilicsurface, those skilled in the art will appreciate that these steps canbe performed separately, e.g., by first forming silicon carbidecontaining layer 104 on dielectric layer 103, then placing the resultingstructure into a PECVD reactor to convert its surface to a hydrophilicsurface.

[0017] To generate the plasma that converts the surface of layer 104 toa hydrophilic surface, a gas that is selected from the group consistingof oxygen, nitrogen, argon, hydrogen, xenon, krypton, nitrous oxide,carbon monoxide, and carbon dioxide may be introduced into reactor 200in the conventional manner. Alternatively, a mixture of helium and oneof these gases may be introduced into reactor 200, or two or more ofthese gases (with or without helium) may be fed into the reactor. Thisgas, or gases, may be introduced into reactor 200 at conventionaltemperatures and pressures. Optimal operating conditions may, of course,depend upon the composition of the gas streams fed into the reactor, thetype of reactor used, and the desired properties for the surface ofsilicon carbide hard masking layer 104. In a preferred embodiment, aplasma is then struck at RF power of between about 100 and about 3,000watts. Any commercially viable frequency, e.g., 13.56 MHz, 27 MHz,microwave frequencies, etc . . . , may be used to generate the plasma.The surface of layer 104 is preferably exposed to that plasma for atleast about 0.5 seconds and for less than about 20 seconds.

[0018] Exposing silicon carbide hard masking layer 104 to such a plasmacan convert its surface from a hydrophobic surface to a hydrophilic one.The depth of that modified surface can be controlled by changing the RFpower, reactor pressure, gas stream composition, susceptor temperature,and/or exposure duration. Optimal operating conditions and gas streammakeup will depend upon the desired properties for the surface of layer104.

[0019] After converting the surface of silicon carbide hard maskinglayer 104 to a hydrophilic surface, photoresist layer 130 may bedeposited onto it, and patterned, to generate the structure representedby FIG. 1b. Because of the hydrophilic nature of the surface of layer104, photoresist layer 130 may bond to that surface in a satisfactorymanner—without requiring the use of an adhesion promoter. Via 107 maythen be etched, followed by removing the photoresist, generating thestructure shown in FIG. 1c. At this stage of the process, via 107 andthe surface of silicon carbide hard masking layer 104 must be cleaned.Because the surface of layer 104 is now hydrophilic, it may be cleanedin the conventional manner, without first requiring its surfacechemistry to be modified with wet chemicals. Following that cleaningstep, conventional process steps are used to remove part of barrierlayer 102 and to fill via 107 with a conductive material. A chemicalmechanical polishing (“CMP”) step may then be applied to remove excessmaterial to form second conductive layer 105, creating the FIG. 1dstructure. Although FIG. 1d illustrates a structure that retains hardmasking layer 104, if desired, that layer may be removed during that CMPstep.

[0020] The method of the present invention may be applied to otherprocesses for forming semiconductor devices. FIGS. 3a-3 c representstructures that may be formed when making a semiconductor device thatincludes a dual damascene interconnect. To make such a device, a secondlayer of photoresist is deposited onto the structure shown in FIG. 1c,then patterned to produce photoresist layer 336, which defines thetrench that will be etched into dielectric layer 303. FIG. 3a representsthe resulting structure. When the surface of silicon carbide hardmasking layer 304 has been previously converted to a hydrophilicsurface, using the technique described above, photoresist layer 336 willbond to hard masking layer 304 in an acceptable fashion.

[0021] After forming photoresist layer 336, trench 306 may be etchedinto dielectric layer 303, as shown in FIG. 3b. Trench 306, via 307, andthe surface of silicon carbide hard masking layer 304 are then cleaned.Because that surface has been converted into a hydrophilic surface, itmay be adequately cleaned using standard cleaning steps. Part of barrierlayer 302 is then removed, followed by filling trench 306 and via 307with a conductive material, then applying a CMP step to remove excessmaterial to form conductive layer 305—generating the FIG. 3c structure.Although this figure shows retention of hard masking layer 304, it maybe removed—if desired.

[0022] Still another process for making a semiconductor device, whichmay benefit from use of the method of the present invention, isillustrated in FIGS. 4a-4 e. In that process, via 407 is filled withsacrificial light absorbing material (“SLAM”) 408 to create thestructure shown in FIG. 4a. That SLAM may comprise a dyedspin-on-polymer (“SOP”) or dyed spin-on-glass (“SOG”) that has dry etchproperties similar to those of dielectric layer 403 and light absorbingproperties that enable the substrate to absorb light during lithography.SLAM 408 may be spin coated onto the FIG. 1c structure in theconventional manner.

[0023] By filling via 407 with SLAM 408, substrate reflection thatoccurs during trench lithography—which could adversely affect dualdamascene via and trench formation—may be reduced or eliminated. Inaddition, filling via 407 with SLAM 408 may eliminate the need to useetch chemistry to etch the trench that is highly selective to dielectriclayer 403 over barrier layer 402, to ensure that the trench etch stepwill not etch through barrier layer 402. When the surface of siliconcarbide hard masking layer 404 has been previously converted to ahydrophilic surface, using the method of the present invention, SLAM 408will bond to hard masking layer 404 in an acceptable fashion.

[0024] A second layer of photoresist may then be deposited onto SLAM408, then patterned to produce photoresist layer 436, which defines thetrench that will be etched into dielectric layer 403, as shown in FIG.4b. Trench 406 is then etched into dielectric layer 403 to produce theFIG. 4c structure. Following that trench etch step, the remainingportions of photoresist layer 436 and remaining portions 409 of the SLAMmust be removed. Photoresist 436 may be removed using a conventionalphotoresist ashing process, or, alternatively, by exposing it to aplasma generated from a forming gas—e.g., a gas that includes up toabout 5% hydrogen in nitrogen, helium and/or argon.

[0025] After removing the photoresist, remaining portions 409 of theSLAM must be removed, along with any residues resulting from thephotoresist removal step. Because the surface of silicon carbide hardmasking layer 404 has been converted into a hydrophilic surface, theremaining portions of the SLAM may be removed, and via 407 and trench406 cleaned, using a standard wet etch step. Part of barrier layer 402may then be removed to generate the structure represented by FIG. 4d.Filling trench 406 and via 407 with a conductive material, then applyinga CMP step to remove excess material to form conductive layer 405,generates the FIG. 4e structure. As indicated above, hard masking layer404 may be removed along with the excess conductive material, ifdesired.

[0026] The process of the present invention provides a convenient andinexpensive way to convert a hydrophobic surface of a silicon carbidelayer into a hydrophilic surface, which can improve that surface'sadhesion properties and make it easier to clean. Although the foregoingdescription has demonstrated how certain processes for makingsemiconductor devices can benefit from the use of this method, themethod of the present invention may be used in many other contexts. Inthis respect, FIG. 5 represents a cross-section of a structure thatincludes silicon carbide containing layer 500 deposited on substrate501. The method of the present invention may be applied to convert ahydrophobic surface of silicon carbide containing layer 500 to ahydrophilic surface, regardless of how substrate 501 is constituted andregardless of the application to which the structure shown in FIG. 5 isemployed.

[0027] Although the foregoing description has specified certain steps,materials, and equipment that may be used in the above described methodfor converting a hydrophobic surface of a silicon carbide containinglayer to a hydrophilic surface, those skilled in the art will appreciatethat many modifications and substitutions may be made. Accordingly, itis intended that all such modifications, alterations, substitutions andadditions be considered to fall within the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A method of converting a hydrophobic surface of asilicon carbide layer to a hydrophilic surface comprising: forming asilicon carbide containing layer on a substrate; then operating a plasmaenhanced chemical vapor deposition reactor to generate a plasma thatconverts the surface of that layer from a hydrophobic surface to ahydrophilic surface.
 2. The method of claim 1 wherein the reactor isfirst operated to form the silicon carbide containing layer on thesubstrate, then operated to generate the plasma that converts thesurface of that layer from a hydrophobic surface to a hydrophilicsurface while the substrate remains in situ inside the reactor.
 3. Themethod of claim 1 wherein the silicon carbide containing layer isexposed to the plasma for at least about 0.5 seconds.
 4. The method ofclaim 3 wherein the silicon carbide containing layer is exposed to theplasma for less than about 20 seconds.
 5. The method of claim 4 whereinthe plasma is generated from a gas that is selected from the groupconsisting of oxygen, nitrogen, argon, hydrogen, xenon, krypton, nitrousoxide, carbon monoxide, and carbon dioxide.
 6. The method of claim 5wherein the plasma is generated from a mixture of helium and at leastone gas that is selected from the group consisting of oxygen, nitrogen,argon, hydrogen, xenon, krypton, nitrous oxide, carbon monoxide, andcarbon dioxide.
 7. The method of claim 6 wherein the plasma is generatedat RF power of between about 100 and about 3000 watts and at anappropriate frequency.
 8. The method of claim 7 wherein the siliconcarbide containing layer includes hydrogen.
 9. A method of forming asemiconductor device comprising: forming on a substrate a siliconcarbide containing layer; introducing into a plasma enhanced chemicalvapor deposition reactor, which contains the substrate that is coveredwith the silicon carbide containing layer, a gas that is selected fromthe group consisting of oxygen, nitrogen, argon, hydrogen, xenon,krypton, nitrous oxide, carbon monoxide, and carbon dioxide; and thenstriking a plasma at RF power of between about 100 and about 3000 watts.10. The method of claim 9 wherein the reactor is first operated to formthe silicon carbide containing layer on the substrate, then operated togenerate a plasma that converts the surface of that layer from ahydrophobic surface to a hydrophilic surface while the substrate remainsin situ inside the reactor.
 11. The method of claim 9 wherein the plasmais struck prior to depositing another material on the surface of thesilicon carbide containing layer.
 12. The method of claim 11 wherein thesilicon carbide containing layer is exposed to the plasma for betweenabout 0.5 seconds and about 20 seconds.
 13. The method of claim 12further comprising depositing a layer of photoresist on the surface ofthe silicon carbide containing layer after the silicon carbidecontaining layer has been exposed to the plasma.
 14. The method of claim13 further comprising depositing a sacrificial light absorbing materialon the surface of the silicon carbide containing layer after the siliconcarbide containing layer has been exposed to the plasma.
 15. A method offorming a semiconductor device comprising: forming on a substrate asilicon carbide hard masking layer; introducing into a plasma enhancedchemical vapor deposition reactor, which contains the substrate that iscovered with the silicon carbide hard masking layer, a gas that isselected from the group consisting of oxygen, nitrogen, argon, hydrogen,xenon, krypton, nitrous oxide, carbon monoxide, and carbon dioxide;striking a plasma at RF power of between about 100 and about 3000 watts;depositing a sacrificial light absorbing material on the surface of thesilicon carbide hard masking layer after it has been exposed to theplasma; and then depositing a layer of photoresist on the sacrificiallight absorbing material.
 16. The method of claim 15 wherein the reactoris first operated to form the silicon carbide hard masking layer on thesubstrate, then operated to generate a plasma that converts the surfaceof that layer from a hydrophobic surface to a hydrophilic surface whilethe substrate remains in situ inside the reactor.
 17. The method ofclaim 15 further comprising introducing helium into the reactor, inaddition to the selected gas, prior to striking the plasma.
 18. Themethod of claim 17 wherein the sacrificial light absorbing material isselected from the group consisting of a dyed spin-on-glass and a dyedspin-on-polymer.
 19. The method of claim 18 wherein the silicon carbidehard masking layer is exposed to the plasma for between about 0.5seconds and about 20 seconds.